
import { useState,useEffect } from "react"
function App() {
    const [count,setCount]=useState(0)
    useEffect(()=>{
        //定义副作用
        document.title = count
    })
  return(
      <div>{count}
          <button onClick={()=>setCount(count +1)}>按钮</button>
      </div>
  )
}

export default App 